This invention relates in general to electronic control modules for anti-lock brake systems and in particular to a heat sink for dispersion of the heat generated by the electronic components included in the control modules.
An Anti-lock Brake System (ABS) is often included as standard equipment on new vehicles. When actuated, the ABS is operative to control the operation of some or all of the vehicle wheel brakes. A typical ABS includes a plurality of solenoid valves mounted within a control valve body and connected to the vehicle hydraulic brake system. Usually, a separate hydraulic source, such as a motor driven pump, is included in the ABS for reapplying hydraulic pressure to the controlled wheel brakes during an ABS braking cycle. The pump is typically included within the control valve body while the pump motor is mounted upon the exterior of the control valve body.
An ABS further includes an electronic control module which has a microprocessor. The control module is electrically coupled to the pump motor, a plurality of solenoid coils associated with the solenoid valves and wheel speed sensors for monitoring the speed and deceleration of the controlled wheels. The control module is typically mounted upon the control valve body to form a compact unit which is often referred to as an ABS electro-hydraulic control unit.
During vehicle operation, the microprocessor in the ABS control module continuously receives speed signals from the wheel speed sensors. The microprocessor monitors the speed signals for potential wheel lock-up conditions. When the vehicle brakes are applied and the microprocessor senses an impending wheel lock-up condition, the microprocessor is operative to actuate the pump motor and selectively operate the solenoid valves in the control unit to cyclically relieve and reapply hydraulic pressure to the controlled wheel brakes. The hydraulic pressure applied to the controlled wheel brakes is adjusted by the operation of the solenoid valves to limit wheel slippage to a safe level while continuing to produce adequate brake torque to decelerate the vehicle as desired by the driver.
The ABS control module typically includes electronic components in addition to the microprocessor which function as actuators for the solenoid valves in the control valve and switching circuits for cycling the pump motor on and off. It is desirable to use discrete electronic components and/or multi-chip hybrid devices which do not have discrete leads but are surface mounted upon a control circuit substrate, such as a printed circuit board or a ceramic substrate. Surface mounting achieves a higher packaging density of the electronic components and/or devices within the control module. This allows a reduction in the overall size of the control module.
The currents drawn through the electronic components in the control module by the pump motor and the solenoid valve windings can be large. Accordingly, many of the electronic components are selected to have high power ratings. During operation of the ABS, the internal resistances of the electronic components generate heat which is transferred to the circuit substrate. The amount of heat generated typically exceeds the capacity of the substrate to dissipate the heat. Thus, additional thermal mass is usually required to assure reliable operation of the control module. Accordingly, a die cast or wrought aluminum heat sink is typically bonded to the control circuit substrate with a thermally conductive adhesive. The adhesive secures the circuit substrate to the heat sink and forms an interface which provides a low thermal resistance path therebetween.